/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Performs any CSG operation between the brush and the world.
0 if nothing happened, 1 if the operation was error-free, or 1+N if N CSG errors occurred.
virtual int32 bspBrushCSG ( [ABrush](API\Runtime\Engine\Engine\ABrush) * Actor, [UModel](API\Runtime\Engine\UModel) * Model, uint32 PolyFlags, EBrushType BrushType, ECsgOper CSGOper, bool bBuildBounds, bool bMergePolys, bool bReplaceNULLMaterialRefs, bool bShowProgressBar )